China Library Classification Number: TH-9 Document Identification Number: A Document Number:1671-7597 (2010) 0420132-01.
With the continuous development of science and technology, mechanical equipment is becoming more and more complex, the level of automation is getting higher and higher, the role and influence of equipment in modern industrial production are getting bigger and bigger, and the expenses related to equipment are getting higher and higher. Any fault or failure in the operation of the machine will not only cause serious consequences, but also cause huge economic losses, and may even lead to catastrophic casualties and bad social impact. By monitoring the working state of machinery and diagnosing its fault development trend at an early stage, we can find out the cause of the fault and take various measures to maintain it, so as to avoid the sudden damage of equipment and make it run safely and economically. It can be seen that equipment fault diagnosis and monitoring technology plays a very important role in modern industrial production, and it is of great practical significance to carry out the research on equipment fault diagnosis technology.
1 Problems in condition monitoring and fault diagnosis of low-speed and heavy-load machinery
1) The most suitable vibration parameter should be selected for low-frequency measurement technology, and the most commonly used parameter for measuring vibration is acceleration. But the acceleration decreases with the decrease of rotation frequency.
2) Low-frequency analysis is limited by measuring equipment, and low rotating speed leads to low frequency of fault vibration signal.
However, the high-pass filter of the sensor will filter out the frequency below 2Hz as noise, and the vibration analysis effect is poor or even impossible due to the influence of environmental noise.
3) The transient problem of impact fault, the time interval between each fault impact is long, and it is difficult to accurately monitor the fault signal by impact method.
4) The impact response frequency generated by the fault point is low, so higher frequency components cannot be aroused.
The difficulties in monitoring low-speed rotating machinery are as follows: when the rotating speed is greater than 600rpm, vibration analysis can be used to diagnose the fault and damage state because of its large vibration energy and short period; For rotating machinery below 600 rpm, it is difficult to diagnose the fault state because of the long period of low-energy vibration. For a long time, low-frequency or even ultra-low-frequency signals (≤2Hz) are beyond the reach of many measuring and analyzing instruments at home and abroad. The measurement of low-frequency vibration signals requires special sensors, measuring instruments and testing methods. The basic task of low-frequency vibration signal testing is to accurately collect fault signals of low-speed equipment. If there is no correct vibration signal, then the later diagnosis work is meaningless. This requires minimizing the electromagnetic interference of sensors and measuring instruments. In addition, there are high requirements for the resolution, measuring range, sampling time and signal processing time of the sensor. High resolution is a necessary condition for measuring low-frequency vibration signals, because the acceleration value of low-frequency vibration may be quite small, for example, when the vibration displacement is 1mm and the frequency is 1Hz, the acceleration value of the signal is only 0.04 m/S2 (0.004 g); The measurement range of the sensor refers to the maximum measurement value that the sensor can measure within a certain nonlinear error range, and signals below or above the measurement range will cause distortion. As a general principle, the higher the sensitivity, the smaller the measurement range; On the contrary, the smaller the sensitivity, the larger the measurement range. The correct acquisition of low-frequency signals must ensure high sensitivity and wide range, so special sensors must be used.
The requirements for measuring instruments are also relatively high. For example, it takes 258 seconds for the equipment to rotate once, so a long sampling time must be set to capture its vibration signal without distortion. If the number of sampling lines is set to 6400 lines and the sampling bandwidth is 0-4000Hz, the data acquisition time must be 96s. So many lines, so wide sampling bandwidth and so long sampling time have high requirements for the signal processing ability and data storage of sampling instruments.
The hidden trouble characteristic frequency of rolling bearing in low-speed and heavy-load equipment is extremely low, generally at the far left of the spectrum, and the vibration energy is small, which is easy to be ignored by diagnostic personnel. Moreover, due to the large vibration of the system itself, the characteristic frequencies of hidden components are submerged, which makes the diagnosis extremely difficult. Traditional spectrum analysis, spectrum thinning and cepstrum techniques can effectively extract potential fault features from strong background noise.
2 Condition monitoring of low-speed and heavy equipment
2. 1 Purpose and task of condition monitoring
The purpose and task of mechanical vibration testing are mainly reflected in the following aspects.
1) can know the running state of mechanical equipment and ensure its running state is within the normal range. Through the continuous detection of mechanical equipment, we can know the running state of the equipment at any time. At the same time, the abnormal operation of machinery reminds people to take remedial measures in time.
2) It can provide an accurate description of the mechanical state. It provides a basis for determining the content and period of equipment maintenance and repair, avoids disassembling the equipment for visual inspection, not only keeps the mechanical integrity in a satisfactory state, but also improves the use efficiency of the equipment.
3) realize predictive maintenance. Through the vibration test, we can accurately grasp the running state of machinery in time, predict the faults and their development trends, and provide technical support for the predictive maintenance of machinery.
2.2 workflow and steps of state monitoring
In the process of monitoring and fault diagnosis of gearbox and bearing, it is always necessary to select the appropriate sensor first and install it at the appropriate measuring point. Because the vibration signal measured by the sensor is weak, the signal measured by the sensor should be connected to the amplifier for amplification, and the signal amplified by the amplifier should be connected to the signal conditioner for preprocessing such as filtering and noise reduction. The signal from the signal conditioner is an analog signal, which cannot be recognized by the computer. Therefore, the vibration signal should be connected to an A/D converter, that is, an A/D card, and converted into a digital signal that can be processed by a computer. Finally, the digital signal is analyzed in time domain and frequency domain by computer, thus the vibration test of gears and bearings is successfully realized.
2.3 Implementation Plan for Condition Monitoring of Low Speed and Heavy Load Machinery
Taking Masteel as the test base, the condition of low-speed and heavy-duty machinery in operation is monitored, including main belt drive drum, reversing drum, hoist reducer, wire rod low-speed blooming mill reducer, mixer idler bearing, rail motor, converter trunnion bearing, converter reducer, vertical mill and so on. The vibration characteristics of this kind of equipment are analyzed. Focus on monitoring the faulty low-speed and heavy-load equipment and make fault diagnosis, including the main belt drive drum, the reduction box of the blooming mill, the support bearing and other transmission parts. Among them, gearbox and bearing seat are fault-prone components. As the key monitoring objects, the fault characteristics are analyzed and the diagnosis methods are studied.
The condition monitoring of low-speed and heavy-duty machinery relies on the dual-channel portable data acquisition instrument RH802, MRS2.0 equipment condition management system and SQL database of Shanghai Rong Zhi Company.
Dual-channel portable data acquisition instrument RH802 has a large-screen LCD display, which is simple in process, small in size, light in weight and convenient to use. The super-large storage capacity can meet the requirements of large-capacity data acquisition, and it can collect planned and unplanned data, and the unplanned data can be saved by number.
MRS2.0 networked management system for equipment condition detection is a networked equipment condition monitoring solution introduced by Rong Zhi Company, and it is a tool for professional technicians to monitor equipment condition and diagnose faults. It organizes multi-level information such as enterprise-factory-workshop-equipment-measuring points in a tree structure.
Management and display, users can quickly and conveniently analyze data in a friendly graphical interface.
MRS2.0 system adopts B/S and C/S structure, and is based on 32-bit Windows software developed by Windows system, which supports Windows.
2000, NT, XP and other operating systems, SQL Server, Oracle, ACCESS and other databases.
In order to study the condition monitoring and fault diagnosis of low-speed and heavy-duty equipment, the database of low-speed and heavy-duty equipment was established with the help of the equipment condition maintenance management system MRS2.0 of Rong Zhi Company.
Add low-speed and heavy-duty machinery to be monitored in the equipment state management system MRS2.0, make the transmission diagram, determine the distribution of measuring points and set the acquisition parameters. Then make a monitoring plan and monitoring cycle. When the monitoring task arrives at the portable data acquisition instrument, it can be monitored on the spot, and the test data is automatically saved in the set path. After the field test is completed, the test data will be uploaded to MRS2.0 equipment status management system for data processing, signal analysis, fault diagnosis and other research work.
3 Conclusion
Based on the fault forms of low-speed heavy-duty machinery (mainly including rolling bearings and gears) in metallurgical industry and the problems existing in condition monitoring and fault diagnosis, this paper focuses on the application of condition monitoring and fault diagnosis technology in low-speed heavy-duty rolling bearings and gears, and studies the characteristics of condition monitoring and fault diagnosis of low-speed heavy-duty units.
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